Making Property sliders act similar to Operators
You can use the 'update' function value that can be assigned to the property's definition:



Update function is triggered each time the slider's value is changing.

import bpy

class SomePanel( bpy.types.Panel ):
    bl_label = "Property panel"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"

    def draw(self, context):
        layout = self.layout
        scn = context.scene
        layout.prop( scn, 'someValue' )

#Update function example:
#self is the object to which you have assigned the property
#context is similar to the context given in the execute function of an operator
def whenUpdate( self, context ):
    if context.active_object:
        context.active_object.location.x = self.someValue
    print( 'update', self.someValue )

def register():
    bpy.types.Scene.someValue = bpy.props.FloatProperty( 
        name = "Float", 
        description = "Enter a float", min = -100, max = 100,
        update = whenUpdate ) #Assign the update function here
    bpy.utils.register_module(__name__)

def unregister():
    bpy.utils.unregister_module(__name__)
    del bpy.types.Scene.someValue

if __name__ == "__main__":
    register()